Norton NRV588 - Rotary Revival

Alternative ideas for improving sportbike performance usually involve yet another arcane front suspension layout like the Bimota Tesi or BMW's Duolever/ Telelever designs-but rarely has anyone offered an alternative engine. Except for the two-stroke, which became a mainstream concept that eventually has been forced into near extinction by environmental concerns, and not counting the current fascination with renewable fuels, there haven't been any truly innovative concepts in gasoline-powered motorcycle engine design. Well, perhaps except for just one: the Wankel rotary.

The Norton Rotary Reborn
It's been 20 years since the rotary engine invented by German engineer Felix Wankel back in 1924 made its motorcycle roadracing debut in 1987. Powering the racebikes of the resurgent Norton factory, the rotary's then-superior performance led to eight years of competition that resulted in successive British roadrace titles, points-scoring GP finishes and victory in the Isle of Man TT against the top superbikes of the day. The fact that each Wankel engine cylinder has only three moving parts that simply rotate-compared with myriad moving pieces in a conventional four-stroke piston engine, many of which run at incredibly high velocities only to stop dead a couple of hundred times a second-makes this a plausibly more efficient mechanical solution. Admittedly, the thorny issue of the bike's exact engine capacity was always a matter of controversy. Because the rotary engine's unique three-sided rotor's power stroke occurs twice during a revolution of the crankshaft (actually called the eccentric shaft, basically a camshaft around which the rotor orbits), some claimed that its displacement should be measured by the single rotor-face-swept area of each of the Norton Wankel's two triangular rotors times two. Nonetheless the rules were massaged on an ongoing basis to make sure the crowd-pleasing Nortons could play their role as British underdogs taking on the might of Japan Inc.

I was able to test each successive year's variant of the Norton rotary racer and found the bikes thrilling to ride, with a good power-to-weight ratio that made them unquestionably fast and with adequate handling. Although the rotary is a dirtier, thirstier design than a conventional four-stroke, it's also lighter and more compact-and potentially more powerful. Just what you need to build a better racebike, as Brian Crighton proved by conceiving the Norton rotary racers that flourished two decades ago. Unfortunately the Nortons withered away after their last race in 1994, thanks to the corporate intrigue that eventually downed the parent company.

But some people never give up, and for 13 years, the 59-year-old Crighton continued to dream of building a Norton rotary racer as light and powerful as he always knew it had the potential to be. Now, with the financial backing of dedicated Norton enthusiast Roy Richards-founder and chairman of Britain's National Motorcycle Museum, where 16 of the 17 Norton factory rotary racers ever made now reside-Crighton's dream has reached reality. The Norton NRV588 is the bike he always wanted to build.

Launched a year ago at Britain's Birmingham Show, and after a season of development held back by the dismal British summer's constant rain, the NRV588 currently produces 165 horsepower at 11,450 rpm from its liquid-cooled twin-rotor engine, yet weighs just 289 pounds with all fluids but fuel. Crighton's ultimate rotary racer offers a power-to-weight ratio comparable to today's factory superbikes, with performance enhanced by current technology that includes a ride-by-wire throttle, fuel injection with a range of usable maps and traction control. "This is the bike I wanted to build for 1995 after we'd beaten the Yamahas and Ducatis plus the RC45 Honda to win the 1994 championship," says Crighton. "I wanted fuel injection for the road bikes to cope with emissions and ride-by-wire throttle to make it easier to ride in the wet via traction control. But they changed the rules to get rid of the Nortons, and anyway the company was fizzling out, so it never got built. But [a British magazine] published an article about my ideas back in August 1994, and when Roy Richards hired me three years ago to restore all his rotary Nortons for the museum, after I'd been working for him for a while I showed him the article. After reading it he said, 'Well, would you like to build it to finish the story off?' He said that he'd finance it personally, and that's how it's come about."

An Old Dog With New Tricks
The heart of the NRV588 is obviously the twin-rotor engine, one of the spare '94 Duckhams motors that incredibly hadn't even been opened and serviced since being built that year. Thus original mechanical spec is unchanged, with 9.6:1 compression and original porting (rotaries control intake and exhaust flow timing via ports, just like a two-stroke). But it's now fitted with fuel injection controlled by an Omex ECU using GEMS software, powered by a Yamaha R6 generator and controlling a single injector per rotor in Crighton's own dual 36mm throttle bodies. These are located beneath the required bulge in the front of the fuel tank to allow space for the tall shower-style injectors; they're necessary to permit usage of the NRV588's variable-intake system (hence the "V" in its designation). But while the concept is similar to the MV Agusta and Yamaha systems, the NRVs feature a linear electric servo motor that controls the movement of the telescopic intake trumpets via a gearbox driving a screw. This allows an actual progressive system, instead of the MV and Yamaha systems that only permit two positions. Plus, while the MV/Yamaha systems only allow a maximum of 75mm of variation in length, the Norton's fully progressive system extends over a huge 120mm range. The trumpets are fully extended at low rpm, then begin to contract from 6000 to 8000 rpm.

Another electric motor controlled by the ECU operates the throttle plates, in a copy of the modular ride-by-wire system on Ducati's MotoGP bikes. This has a conventional throttle cable running from the grip to a potentiometer, which translates the action in digital form to the ECU. The ECU then instructs the electric motor to operate the butterflies according to a preprogrammed map that can be altered depending on weather, track conditions, tire wear and so on.

A belt primary drive transfers power from the rotary's eccentric shaft (the Wankel's "crankshaft") to the separate Yamaha OW01 six-speed transmission. Although difficult to distinguish in this photo, the actual rotary engine is very compact, with an overall size not that much larger than the oversize ignition rotor. Note the oil-injection pump (the rotary is like a two-stroke in that its combustion components are lubricated by oil in the intake charge) driven off the clutch shaft.

An Ohlins inverted superbike fork rides on an ultralight 16.5-inch Dymag carbon-fiber wheel shod with Dunlop racing rubber, with radial-mount, monoblock, four-piston AP calipers biting down on 320mm steel discs. The extra-large radiator is necessary to shed the rotary's intense heat production.

These two shots show the Norton's innovative variable-intake system in full extension and retraction. Unlike the similar systems used on the Yamaha R1 and MV Agusta F4 CC, the NRV588's unit is a fully progressive-length system. Note also that as the intake stacks move through their 120mm range of travel (the Yamaha and MV systems only allow a maximum of 75mm), the shower-style injector towers follow in synchronized movement.

Having ridden both four-cylinder sportbikes fitted with variable-intake systems, I was interested to see how this would work on the rotary engine. I remembered from my several previous Norton rides that it had a broad spread of power but suffered from a lack of low-end torque, especially if tuned for top-end power like the original bikes were. That always made them even more like a two-stroke to ride, and the heavier flywheel required to tame the otherwise explosive powerband also tended to compromise acceleration, only partially rectified by the bike's light weight.

The NRV588 has no such problem. For example, compared with Steve Hislop's TT-winning ABUS Norton, which had a nice midrange but was definitely peaky in terms of power delivery, the new bike feels like it's powered by an extremely potent electric motor. There's a huge range of seamless, linear power from 3000 rpm all the way up to the 11,500-rpm rev limiter. Throttle response is crisp without being abrupt, a welcome trait considering the NRV's high power output and light weight. The 2D LCD dash is hard to read because of the lack of contrast in daylight and the smallish numbers, and the engine is so smooth that you have no sense of feel that it's time to shift. This caused me to bump into the rev limiter often; a bright shift light would help here. The excellent low-end torque meant that driving out of the tight turns could be done in second gear-no need for first gear in the separate six-speed Yamaha OW01 gearbox with belt primary drive. However, there's no power shifter fitted to the race-pattern gearshift, because the engine's relatively heavy flywheel and long gear spacing make it difficult to prevent shock loading while shifting through the lower gears.